Vehicle power transmission of this type is well known to the art as disclosed in, for example, U.S. Pat. Nos. 3,812,735 and 4,103,566 and is particularly suitable for use in small-scaled working vehicles because such transmission is compact in scale. Another advantage is that a transmission of this type permits a straight line shift patern so that a remote control change lever may be employed with ease.
In the past, a mechanical clutch is employed for the purpose of interrupting input of power to the transmission before a shifting operation by a change lever is performed. A typical example of such mechanical clutch is a belt-tightening clutch in which a tightening pulley in a belt drive is supported so that it may be displaced away from a belt for disactuating the belt drive.
Such mechanical clutch may damage a gear-engaging clutch portion of shift key because a mechanical clutch allows a transmission shaft, with which the shift key is associated, to be put suddenly into a normal speed rotation when the clutch is actuated or engaged again after a shifting operation. Such damage of gear-engaging clutch portion is considerable when the mechanical clutch is re-engaged after a shift-down operation too early, because inertial rotation of shaft due to a higher speed ratio rotation before such shift-down will provide a large load to the clutch portion.
Accordingly, a primary object of the present invention is to provide an improved transmission of the type set forth before in which a fluid-actuated clutch is employed in combination with a fluid supply system therefor for protecting clutch portion of a shift key from damage.
An attendant object of the invention is to provide a novel transmission in which the fluid supply system set forth above includes an unloader valve employed for controlling the operation of fluid-actuated clutch in a reliable and simple fashion.
Another attendant object is to provide a novel transmission in which the fluid supply system set forth above includes a simple valve means which controls both of fluid pressure applied to fluid-actuated clutch and operation itself of such clutch.
A furtherobject of the present invention is to provide a novel transmission in which a differential-locking clutch is employed which is operated by fluid provided from the fluid supply system set forth above.